Inverter circuit



Patented June 16, 1942 INVERTER CIRCUIT Harold J. Brown, Indianapolis, Ind., asslgnor to Electronic Laboratories, Incorporated, Indianapolis, Ind., a corporation of Indiana Application September 23, 1940, Serial No. 357,878

Claims.

The present invention relates to electric systems primarily for converting direct current into alternating current by means of a vibratory switch.

More specifically, means for improving the contact engagement of the vibratory switch of an inverter of the vibratory switch type adapted for converting direct current into alternating current.

One serious difliculty which has heretofore been encountered in inverters of the vibratory switch type is that of the relatively short length of the life of the switch contacts. Due to the fact that in an apparatus of this character the contacts open and close at extreme rapidity so that the circuit ismade and broken a large number of times throughout the life of the apparatus and due to the character of the load carried by these contacts, etc, the contacts rapidly become pitted and deteriorated. This, of course, de-

creases materially the life of the switch and, furthermore, decreases the operative value of the switch. After the contacts have become slightly pitted there is always danger of the contacts sticking, resulting in the device becoming inoperative.

In connection with vibrator type inverters or converters, there is a need for increased power output capabilities. By using larger transformers and larger vibrators, increased output has been obtained, but in general, a less satisfactory result is noted, especially as regards vibrator life and reliability. Vibrators with several sets of points in parallel have also been used in an efiort to increase the power handling capacities, but here too, the life and reliability of the unit does not come up to expectation. The principal reason for the lack of satisfactory results lies in the character of the contacting materials when interrupting current. Generally speaking, the current in a contact necks down to an extremely high current density prior to separation, even though large shunting capacities be used. For reasonable values of current relative to the material used, the contact is subject to melting and vaporization at the final tip, and if two or more contacts are in parallel, the single final trailing contact is subject to the attack of this high current density. Similar destructive effects take place when the contact engagement is made, as the condensers necessary to operate the equipment are then charged or discharged. One of the more noticeable effects is material transfer from one contact to the other, another is pitting and the invention relates to erosion, and in severe cases, there is arcing which is very destructive.

A characteristic of contact devices, is that various thresholds of current exist below which material transfer and erosion do not occur at all or in small amounts.

It is one of the objects of my invention to provide an electric system embodying a vibrating switch wherein means is provided for pre venting deterioration of the contacts of the switch and insuring long life to the apparatus as well as insuring reliability in the operation thereof.

Another object of my invention is to forcibly prevent the current flowing in two or more vibrator contacts from re-establishing itself in a single final trailing contact tip during a vibratory movement, as is the usual case.

Another object of my invention is the provision, in a vibratory interrupter having a plurality of parallel interrupting paths, of preventing the current which is interrupted in an interrupted path incident, to slight variations in the breaking of the plurality of contact means from suddenly reestablishing itself in a yet uninterrupted path during a vibratory interval of the breaking of 'the plurality of contact means.

Another object of my invention is to keep the flow of the interrupting current in the interrupting contacts less than certain threshold values below which material transfer and erosion of the contacts do not occur at all or in small amounts.

For the purpose of disclosing the invention, I have illustrated an embodiment thereof in th accompanying drawing in which:

Fig. l is a diagrammatic view of a circuit arrangement embodying my invention;

Fig. 2 a diagrammatic view of a modified circuit embodying my invention; and

Fig. 3 is a more or less diagrammatic view of the type of transformer disclosd in the circuit arrangement illustrated in Fig. 2.

In the arrangement disclosed, I provide a transformer including a primary coil l and a secondary coil 2. The primary coil I has a center tap 3 connected to one side of a source of direct current 4 which may be, as is illustrated in the drawing, a battery. The opposite terminals of the coil l are respectively connected to pairs 5, 5 and 6, 6 of stationary contacts disposed on opposite sides of a vibrator switch including simultaneously moving vibrator reeds l, I. These reeds the battery 4.

Each reed has connected in series therewith 1 an inductance 8, 8 and connected in effective electrical shunt relation with each of the makeand-break contactspf the parallel interrupting paths is a capacitor 9,. 9.

The reeds are, in actual practice, mechanically connected together but electrically insulated from each other and are vibrated in unison through the instrumentality of an electromagnet Ill having a winding H, one terminal of which is connected to a terminal of the battery 4, With the electromagnet l deenergized, one of the reeds I will normally be in contact with the contact I3. Therefore, as soon as the circuit through the winding II is closed, the electromagnet will be energized, setting the reeds I, 1 in vibratory motion. The initial impulse of the magnet l0 will be to attract these reeds to ward the magnet, thereby causing the reeds I, 1 to contact with the pair of contacts 5, 5 closing a circuit through one portion of the primary l in one direction and, at'the same time, opening the circuit of the magnet In at the contact i3. The deenergization of the magnet Ill, of course, will permit the reeds 1, 1 to, under the normal frequency of the reeds, move in the opposite direction until they engage the contact 6,6, and also the contact 13. The engagement of the contact 6, 6 by the reeds will close the circuit through the other portion of the winding of the primary in the opposite direction, thereby inducing an alternating current in the secondary -2 of the transformer.

It is to be noted that the contacts controlling the circuits through the primary are arranged in parallel and that the circuit arrangement is such that a capacitor or condenser is connected in effective electrical shunt relation with each of the make-and-break contacts and in series with each of the parallel interrupting paths there is provided an inductive impedance.

As a result of this arrangement the current, during the interval the contacts are closed, is not carried by a single contact but is carried by a pair of contacts arranged in parallel. Therefore the load adapted to be carried by each contact is divided during the interval the contacts are closed. However, I have found from experience that it is impossible to insure the absolute simultaneous breaking of the contacts and therefore while the load carried by the contacts is reduced, during the interval that the contacts are closed, the arcing and destructive influence of the circuit are not prevented by merely dividing the contacts or providing a pair of contacts instead of one. With merely a pair of contacts instead of one contact, the arcing would be at a maximum over that contact breaking last, that is the single final trailing tip. However, by the provision of the capacitor or condenser 9 connected in effective electrical shunt relation with each of the make-and-break contacts and by the provision of the inductive impedance 8 in series with each of the parallel interrupting paths which develops an inductive impedance to the flow of current through the trailing engaged or yet uninterrupted contacts of a vibratory movement, I am enabled to not only reduce the load carried by each contact but to prevent arcing of the contacts at the time of breaking.

In the structure illustrated in Figs. 2 and 3, I have shown a modified circuit and a transformer embodying my invention. In this arrangement a single vibrating reed l4 connected to one terminal of the battery I5 is provided. This reed, in its vibratory movement, is adapted to engage a pair of stationary contacts II and I1 connected, respectively, to one terminal of a primary winding lland one terminal of a primary winding is. A second pair of stationary contacts 20 and 2| connected, respectively, to the terminals of the windings I 8 and I l are engaged by the reed in its movement in the opposite direction from its engaging movement for contacts l6 and H. Each of the windings I8 and I9 are provided with a center tap adapted to be connected to the opposite terminal of the battery IS.

The reed is vibrated in the same manner as that illustrated with respect to Fig. 1 through the instrumentality of an electromagnet l I having its circuit controlled through the reed and a stationary contact l3.

It is to be noted that in this structure, instead of providing a specific type of inductive impedance in series, as is the case in the arrangement illustrated in Fig. 1, with each of the pairs of contacts I rely on the leakage inductances developed as the result of the particular construction and arrangement of the transformer coils as shown in Fig. 3.

As a result of this arrangement I am enabled to obtain substantially the same results as with the structure illustrated in Fig. 1 and am enabled to provide a means for developing an inductance in series with each of the parallel interrupting paths as well as to associate with the different make-and-break contacts a'condenser which, in combination with' the inductive impedance, assures the division of the currents during the breaking of the contacts.

Both forms of my invention are directed to an arrangement for preventing the current which is interrupted in an interruptedpath incident to slight variationsin the breaking of the plurality of contact means from suddenly re-establishing itself in a yet uninterrupted path during a vibratory interval of the breaking of the plurality of contact means, in which the arrangement comprises the combination of a capacitor connectedin effective electrical shunt relation with each of the make-and-break contact means, and inductance means for developing, in series with each of the parallel interrupting paths, an inductive impedance to the flow of the current therein, the inductive impedance in the yet uninterrupted path opposing the sudden re-establishment of the current of an interrupted path during a vibratory interval in the yet uninterrupted path, thereby preventing the damaging of the contact means. The value of the circuit constants are such that currents flowing in either element cannot be divertedfrom one reed to the other in the length of time between consecutive openings of the normally parallel contacts, and therefore true division of current exists.

I claim as my invention:

1. In an electrical system for converting direct current into alternating current, said system having a transformer with input and output winding means and a vibratory interrupter having a plurality of parallel interrupting paths each having make-and-break contact means substantially simultaneously operated during a vibratory interval for jointly supplying an interrupted direct current to the input winding means of the transformer; the arrangement for preventing the current which is interrupted in an interrupted path incident to slight variations in the breaking of the plurality of contact means from suddenly re-establishing itself in a yet uninterrupted path during a vibratory interval of the breaking of the plurality of contact means, said arrangement comprising the combination of a capacitor connected in effective electrical current-diverting shunt relation with each of the make-and-break contact means, and inductance means for developing, in series with each of the parallel interrupting paths, an inductive impedance to the flow of the current therein, the inductive impedance in the yet uninterrupted path opposing the sudden reestablishment of the current of an interrupted path during a vibratory interval in the yet uninterrupted path, thereby preventing the damaging of the contact means.

2. In an electrical system for converting direct current into alternating current, said system having a transformer with input and output winding means and a vibratory interrupter having a plurality of parallel interrupting paths each having make-and-break contact means substantially simultaneously operated during a vibratory interval for jointly supplying an interrupted direct current to the input winding means of the transformer; the arrangement for preventing the current which is interrupted in an interrupted path incident to slight variations in the breaking of the plurality of contact means from suddenly re-establishing itself in a yet uninterrupted path during a vibratory interval of the breaking of the plurality of contact means, said arrangement comprising the combination of a capacitor connected in effective electrical current-diverting shunt relation with each of the make-and-break contact means, and inductance means for developing, in series with each of the parallel interrupting paths, an inductive impedance to' the flow of the current therein, the inductive impedance in the yet uninterrupted path opposing the sudden re-establishment of the current. of an interrupted path during a vibratory interval in the yet uninterrupted path, thereby preventing the damaging of the contact means, said inductance means comprising an inductance element connected in series with each of the make-and-break contact means.

3. Inpan electrical system for converting direct current into alternating current, said system having a transformer with input and output winding means and a vibratory interrupter having a plurality of parallel interrupting paths each having make-and-break contact means substantially simultaneously operated during a vibratory interval for jointly supplying an interrupted direct current to the input winding means means in the transformer for developing, in series with each of the parallel interrupting paths, an inductive impedance to the flow of the current therein, the inductive impedance in the yet uninterrupted path opposing the sudden re-establishment of the current of an interrupted path during a vibratory interval in the yet uninterrupted path, thereby preventing the damaging of the contact means.

. 4. An electrical system for converting direct current into alternating current cwiprising, in combination, a transformer having a core with at least two input windings thereon and an output winding thereon disposed between the two input windings, a vibratory. interrupter having an interrupting path for each of the input windings of the transformer, each of said interrupt ing paths having make-and-break contact means therein to separately supply an interrupted direct 'current to each of the input windings. of the transformer, means for operating the make-andbreak contact means substantially simultaneously, and a capacitor connected in effective electrical current-diverting shunt relation with each of the make-and-break contact means, the leakage reactance of each of the input windings opposing the flow of current in the interrupting paths respectively, the leakage reactance in the yet uninterrupted path incident to slight variations in the breaking of the contact means opposing the sudden re-establishment of the current of an interrupted path during a vibratory interval of the breaking of the contacts in the yet uninterrupted path, thereby preventing the damaging of the contact means.

5. In an electrical system for converting direct current into alternating current, said system including a vibratory interrupter having a plurality of parallel interrupting paths each having makeand-break contact means substantially simultaneously operated during a vibratory interval for jointly supplying. an interrupted direct current to the said system; the arrangement for preventing the current which is interrupted in an interrupted path incident to slight variations in the breaking of the plurality of contact means from suddenly re-establishing itself in a yet uninterrupted path during a vibratory interval of the breaking of the plurality of contact means, said arrangement comprising the combination of a transformer having input winding means conof the transformer; the arrangement for preventing the current which is interrupted in an interrupted path incident to slight variations in the breaking of the plurality of contact means from suddenly re-establishing itself in a yet uninterrupted path during'a vibratory interval of the breaking of the plurality of contact means,

- said arrangement comprising the combination of nected in circuit relation with the vibratory interrupter and energized by the interrupted direct current, a capacitor connected in effective electrical current-diverting shunt relation with each of the make-and-break contact means, and inductance means for developing, in series with each of the parallel interrupting paths, an inductive impedance to the flow of the current therein, the inductive impedance in the yet uninterrupted path opposing the sudden re-establishment of the current of an interrupted path during a vibratory interval in the yet uninterrupted path, thereby preventing the damaging of the contact means.

HAROLD J. BROWN. 

